Arthropods are a source of, or transmit, many diseases and conditions in humans and other animals. Some arthropods may simply cause localized irritation of the skin without transmission of disease, such as occurs with mites and ticks, or by transmission of disease-causing pathogens such as arboviruses, protozoa, bacteria and nematodes. These disease-causing pathogens are responsible for a variety of different diseases of humans and other animals including malaria, Dengue fever, Eastern Equine encephalitis, Western Equine encephalitis, Venezuelan equine encephalitis, Japanese encephalitis, Murray Valley encephalitis, West Nile fever, Yellow fever, LaCrosse encephalitis Asian spotted fever, Q fever, Lymphatic filariasis (Elephantiasis), Chikungunya fever, Ross river fever and Chagas disease.
Most pathogens that are transmitted by mosquitoes share a common property; they have to undergo a significant period of development in their insect vector before they can be transmitted to a new host. After a female mosquito ingests an infectious blood-meal, parasites or arboviruses, such as dengue, penetrate the mosquito's midgut and replicate in various tissues before infecting the salivary glands, where they are transmitted to a new host during subsequent blood-feeding. This time period from pathogen ingestion to potential infectivity is termed the extrinsic incubation period (EIP), and lasts approximately two weeks for both dengue (Siler et al., 1926; Watts et al., 1987) and malaria (Gilles et al., 2002). A female mosquito must survive longer than its initial non-feeding period (usually less than 2 days) plus the EIP to successfully contribute to pathogen transmission. Mosquito survival is therefore considered a critical component of a vector population's capacity for pathogen transmission (Dye, 1992). Interventions that aim to reduce the daily survivorship of adult mosquitoes, such as the spraying of residual insecticides in houses and insecticide-treated bednets for malaria control, yield large reductions in pathogen transmission rates (Masabo et al., 2004; Schellenberg et al., 2001) because of the sensitive relationship between mosquito survival and vectorial capacity (Garrett-Jones, 1964; MacDonald, 1957).
The control of diseases such as dengue primarily targets Aedes aegypti, a domesticated mosquito that prefers to live in and around human habitation (Gubler et al., 1997). With few exceptions, dengue management strategies have been complicated by the inability to completely eradicate A. aegypti from urban settings, and the ineffective application of long lasting vector control programs (Morrison et al., 2008). This has led to a worldwide resurgence of dengue, and highlighted the urgent need for novel and sustainable disease control strategies.
A strain of the obligate intracellular bacterium Wolbachia pipientis, wMelPop, has been described that reduces adult lifespan of its natural fruit fly host Drosophila melanogaster (Min and Benzer, 1997). Wolbachia are maternally-inherited bacteria that use mechanisms such as cytoplasmic incompatibility (CI), a type of embryonic lethality that results from crosses between infected males with uninfected females, to rapidly spread into insect populations (Hoffmann and Turelli, 1997).
However, life-shortening Wolbachia strains do not occur in mosquitoes naturally and experimental transfer of Wolbachia between host species (transinfection) has lacked success (Van Meer and Stouthamer, 1999). In some cases, transferred strains can be stable and maternally inherited, primarily when Wolbachia is transferred within or between closely related species in a family or genus (Boyle et al., 1993; Xi et al., 2005; Zabalou et al., 2004). In other cases, the new infection appears poorly adapted to its new host, showing fluctuating infection densities and variable degrees of transovarial transmission. The result is often loss of infection within a few host generations. Wolbachia infections tend to be more susceptible to loss when they have been transferred between phylogenetically distant hosts (Kang et al., 2003; Riegler et al., 2004). Similarly, those species that do not naturally harbour Wolbachia have proven refractory to transinfection (Curtis and Sinkins, 1998; Rigaud et al., 2001).